Can you paste your conversion code? provide more detail?
I am using the "Insert\Edit link" UI icon from the Admin backend to try and convert it. In anycase, here is the source code after I tried to convert and publish it.
<p>Website<br /><a href="https://www.abcd.com/:443/EPiServer/CMS/Content/en/,,1417/?epieditmode=False" target="_blank" rel="noopener">www.abcd.com</a></p>
Razor code showing what you are using the render that link would be more useful.
It will be something like <p>Website<br /> @Html.PropertyFor(m => m.YourLink)</p>
I am facing an issue where a site on EPiServer 7.5 base is hosted on the IIS 8.5 and when I am trying to convert a text to hyperlink to point to an external link, it adds postscript to it (like - :443/EPiServer/CMS/Content/en/,,1417/?epieditmode=False) causing the webpage to show 404 not found when user clicks on it. I believe it's similar to this old thread in the Forum which is marked as resolved but I have already tried the resolution and it doesn't work -
EPiServer CMS 7.6.3(7.5) Edit mode preview is redirected to 404 on IIS 8.5
If someone has found an alternate solution to this, it would be really helpful.